Vehicle drive device

ABSTRACT

To provide a vehicle drive device capable of efficiently driving a vehicle by using a motor without falling into the vicious cycle between enhancement of driving via the motor and an increase in vehicle weight. The present invention is a vehicle drive device ( 10 ) having a motor for driving the wheels of a vehicle and includes a front wheel motor ( 20 ) for driving front wheels ( 2   b ) of a vehicle ( 1 ) and a battery ( 18 ) and a capacitor ( 22 ) that supply electric power for driving the front wheel motor ( 20 ), in which the voltage of the battery ( 18 ) and the capacitor ( 22 ) connected in series is applied to the front wheel motor ( 20 ) and the capacitor ( 22 ) is disposed between the left and right front wheels ( 2   b ) of the vehicle ( 1 ).

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is based on PCT filing PCT/JP2019/011430, filedMar. 19, 2019, which claims priority to JP 2018-052636, filed Mar. 20,2018, and JP 2018-143357, filed Jul. 31, 2018, the entire contents ofeach are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a vehicle drive device and, moreparticular to a vehicle drive device having a motor that drives wheelsof a vehicle.

BACKGROUND ART

In recent years, exhaust gas regulations for vehicles have been enhancedand demands for fuel efficiency and carbon dioxide emissions per traveldistance for vehicles have become strict in various countries in theworld. In addition, some cities regulate entry of vehicles travelinginternal combustion engine into urban areas. To satisfy these requests,hybrid-drive vehicles having an internal combustion engine and motorsand electric vehicles driven only by motors have been developed andwidely used.

Japanese Patent No. 5280961 (PTL 1) describes a drive control device forvehicles. In this drive control device, a drive device is provided onthe rear wheel side of the vehicle and two motors provided in this drivedevise drive the rear wheels of the vehicle, respectively. In additionto drive device, a drive unit formed by connecting an internalcombustion engine and a motor are in series is provided in the frontportion of the vehicle. The power of the drive unit is transmitted tothe front wheels via the transmission and the main drive shaft and thepower of the drive device is transmitted to the rear wheels of thevehicle. In addition, in this drive control device, the two motors ofthe drive device are driven when the vehicle starts, and these drivingforces are transmitted to the rear wheels of the vehicle, respectively.In addition, the driving unit also generates a driving force duringacceleration of the vehicle and the four-wheel drive is achieved by thedriving unit and the two motors of the drive device. As described above,in the drive control device described in PTL 1, the two motors providedmainly for the rear wheels of the vehicle generate the driving forces.

CITATION LIST Patent Literature

PTL 1: Japanese Patent No. 5280961

SUMMARY OF INVENTION Technical Problem

Since the driving of a vehicle by motors does not emit carbon dioxideduring a travel, emission regulations that are enhanced each year can beadvantageously satisfied, but it is difficult to ensure a sufficientlylong distance travel because the electric power that can be stored inthe battery is limited. Accordingly, a hybrid drive device having aninternal combustion engine together with motors is widely used as adrive device for vehicles. In addition, even in such a hybrid drivedevice, in order to reduce carbon dioxide emissions during a travel,vehicles that mainly utilize the driving forces of motors like thevehicle described in PTL 1 are increasing.

Such a hybrid drive device driven mainly by the driving forces of motorsas described above needs to have a large capacity battery to obtainsufficient travel performance. In addition, in order to obtain asufficient driving forces by motors, the motors need to be operated at arelatively high voltage. Accordingly, in a hybrid drive device drivenmainly by the driving forces of motors, since a large capacity batteryis necessary and the electrical system that supplies a high voltage tothe motors needs to be electrically insulated sufficiently, the overallweight of the vehicle increases and the fuel efficiency of the vehiclereduces. Furthermore, in order to drive the vehicle with a heavy weightby the motors, a larger capacity battery and a higher voltage arerequired, thereby causing a vicious cycle that further increases theweight.

In particular, when high output power is obtained while the voltage fordriving the motor is kept low, since the cross section area of aconductor for supplying electric power needs to be increased due to anincrease in the current for driving the motor, thereby causing anincrease in weight and cost. In contrast, when high output power isobtained while the current for driving the motor is kept low, the powersupply voltage needs to be increased, this high voltage requests thepower supply system for transmitting electric power to the motor to havehigh insulation performance, thereby leading to an increase in weightand cost.

Accordingly, an object of the present invention is to provide a vehicledrive device capable of efficiently driving a vehicle by using motorswithout falling into the vicious cycle between enhancement of driving bymotors and an increase in vehicle weight.

Solution to Problem

To solve the problem described above, according to the presentinvention, there is provided a vehicle drive device having a motor fordriving wheels of a vehicle, the vehicle drive device including a frontwheel motor for driving front wheels of the vehicle; and a battery and acapacitor that supply electric power for driving the front wheel motor,in which a voltage of the battery and the capacitor connected in seriesis applied to the front wheel motor, and the capacitor is disposedbetween the left and right front wheels of the vehicle.

In the present invention configured as described above, the voltage ofthe battery and the capacitor connected in series is applied to thefront wheel motor and the front wheel motor drives the front wheels ofthe vehicle. The capacitor is disposed between left and right wheels ofthe vehicle.

In the present invention configured as described above, since thevoltage of the battery and the capacitor connected in series is appliedto the front wheel motor, even when a low voltage battery is used, thefront wheel motor can be driven by a higher voltage. This can keep thecurrent for driving the front wheel motor low and prevent the conductorfor supplying electric power from becoming excessive. On the other hand,since a high voltage is applied to the front wheel motor from thebattery and the capacitor connected in series, the dielectric withstandvoltage of a high voltage portion needs to be high. However, since thefront wheel motor is close to the capacitor disposed between the leftand right wheels of the vehicle, the route requested for a highdielectric withstand voltage becomes short and an increase in weight andcost can be minimized.

In the present invention, preferably, the capacitor is disposed at aposition at which at least a part of the capacitor overlaps with thefront wheels when viewed from a side of the vehicle.

In the present invention configured as described above, since thecapacitor is disposed at a position at which at least a part of thecapacitor overlaps with the front wheels when viewed from the side ofthe vehicle, the electric power supply path from the capacitor to thefront wheel motor can be further shortened, thereby further suppressingan increase in weight and cost caused by the insulating member.

In the present invention, preferably, the vehicle drive device furtherincludes an internal combustion engine that drives the vehicle, in whichthe capacitor is disposed in front of the internal combustion engine sothat at least a part of the capacitor overlaps with the internalcombustion engine when viewed from a front of the vehicle.

In the present invention configured as described above, since thecapacitor is disposed in front of the internal combustion engine, if thevehicle collides from the front, the capacitor is damaged first. Thecapacitor is generally made of a material that does not burn easily.Accordingly, even if the vehicle collides, since the flame-retardantcapacitor suppresses damage to the internal combustion engine, thesafety of the vehicle can be further enhanced.

In the present invention, preferably, the front wheel motor includesin-wheel motors provided in the left and right front wheels of thevehicle, respectively.

In the present invention configured as described above, since the frontwheel motor includes in-wheel motors, the drive shafts that connect thefrom wheel motor and the wheels can be eliminated or shortened, therebymaking the vehicle more lightweight.

In the present invention, preferably, the battery is disposed below avehicle interior of the vehicle or in a rear portion of the vehicle.

In the present invention configured as described above, since thebattery is disposed below the vehicle interior of the vehicle or in therear portion of the vehicle, even if the vehicle collides from thefront, the impact of the collision does not easily affect the batteryand damage to the battery can be suppressed.

In the present invention, preferably, a maximum inter-terminal voltageof the capacitor is set to a voltage higher than an inter-terminalvoltage of the battery.

In the present invention configured as described above, since themaximum inter-terminal voltage of the capacitor is higher than theinter-terminal voltage of the battery, the voltage applied to the frontwheel motor can be sufficiently high and sufficient output power can beobtained while the current flowing to the front wheel motor issuppressed.

In the present invention, preferably, the vehicle drive device furtherincludes a first voltage converting unit connected between the capacitorand the battery, in which the first voltage converting unit performs atleast one of an operation that raises the voltage of the battery andcharges the capacitor with electric power stored in the battery and anoperation that lowers the voltage of the capacitor and charges thebattery with electric power stored in the capacitor.

In the present invention configured as described above, since thevehicle drive device includes the first voltage converting unit thatcharges the capacitor with the electric power stored in the battery orcharges the battery with the electric power stored in the capacitor, theamounts of electric power stored in the battery and the capacitor can beadjusted and the electric power stored in the battery and the capacitorcan be used effectively.

In the present invention, preferably, the vehicle drive device furtherincludes a second voltage converting unit connected between the batteryand an electric component provided in the vehicle, in which the secondvoltage convening unit lowers the voltage of the battery and supplieselectric power to the electric component.

In the present invention configured as described above, since the secondvoltage converting unit lowers the battery voltage and supplies electricpower to the electric component, the battery used to drive the frontwheel motor can be shared with the electric component and the vehiclecan be made lightweight.

Advantageous Effects of Invention

The vehicle drive device according to the present invention canefficiently drive a vehicle using a motor without causing the viciouscycle between enhancement of driving by the motor and an increase invehicle weight.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a layout diagram illustrating a vehicle in which a hybriddrive device according to a first embodiment of the present invention isinstalled.

FIG. 2 is a perspective view, as seen from above, illustrating a frontportion of the vehicle in which the hybrid drive device according to thefirst embodiment of the present invention is installed.

FIG. 3 is a perspective view, as seen from the side, illustrating thefront portion of the vehicle in which the hybrid drive device accordingto the first embodiment of the present invention is installed.

FIG. 4 is a sectional view taken along line iv-iv in FIG. 2 .

FIG. 5 is a block diagram illustrating the inputs and outputs of varioussignals in the hybrid drive device according to the first embodiment ofthe present invention.

FIG. 6 is a block diagram illustrating the power supply structure of thehybrid drive device according to the first embodiment of the presentinvention.

FIG. 7 is a diagram schematically illustrating one example of changes involtages when electric power is regenerated into a capacitor in thehybrid drive device according to the first embodiment of the presentinvention.

FIG. 8 is a diagram illustrating the relationship between the outputpower and the vehicle speed of individual motors used in the hybriddrive device according to the first embodiment of the present invention.

FIG. 9 is a sectional view schematically illustrating the structure ofan auxiliary drive motor adopted in the hybrid drive device according tothe first embodiment of the present invention.

FIG. 10 is a flowchart illustrating control by a control device of thehybrid drive device according to the first embodiment of the presentinvention.

FIG. 11 is a graph illustrating examples of operations in individualmodes of the hybrid drive device according to the first embodiment ofthe present invention.

FIG. 12 is a diagram schematically illustrating changes in theacceleration acting on the vehicle when a transmission downshifts orupshifts in the hybrid drive device according to the first embodiment ofthe present invention.

DESCRIPTION OF EMBODIMENTS

Next, preferred embodiments of the present invention will be describedwith reference to the attached drawings.

FIG. 1 is a layout diagram illustrating, a vehicle in which a hybriddrive device according to a first embodiment of the present invention isinstalled. FIG. 2 is a perspective view, as seen from the side,illustrating the front portion of a vehicle in which the hybrid drivedevice according to the embodiment is installed and FIG. 3 is aperspective view, as seen from the side, illustrating the front portionof the vehicle. FIG. 4 is a sectional view taken along line iv-iv inFIG. 2 .

As illustrated in FIG. 1 , a vehicle 1 having the hybrid drive system,which is a vehicle drive device according to the first embodiment of thepresent invention, is a so-called FR (front engine rear drive) vehiclein which an engine 12 as an internal combustion engine is installed inthe front portion (in front of the driver's seat) of the vehicle and apair of left and right rear wheels 2 a as main drive wheels is driven.In addition, as described later, the rear wheels 2 a are also driven bythe main drive motor, which is the main drive electric motor, and a pairof left and right front wheels 2 b, which are auxiliary drive wheels, isdriven by the auxiliary drive motors, which are the auxiliary driveelectric motors.

A hybrid drive device 10 according to the first embodiment of thepresent invention installed in the vehicle 1 includes the engine 12 thatdrives the rear wheels 2 a, a power transmission mechanism 14 thattransmits a driving force to the rear wheels 2 a, a main drive motor 16that drives the rear wheels 2 a, a battery 18 that is an electricstorage unit, auxiliary drive motors 20 that drive the front wheels 2 b,a capacitor 22, and a control device 24 that is a controller.

The engine 12 is an internal combustion engine for generating a drivingforce for the rear wheels 2 a, which are the main drive wheels of thevehicle 1. As illustrated in FIGS. 2 to 4 , in the embodiment in-line4-cylinder engine is adopted as the engine 12 and the engine 12 disposedin the front portion of the vehicle 1 drives the rear wheels 2 a via thepower transmission mechanism 14. In addition, as illustrated in FIG. 4 ,in the embodiment, the engine 12 is a flywheel-less engine that does notinclude a flywheel and installed on a subframe 4 a of the vehicle 1 viaengine mounts 6 a. Furthermore, the sub-frame 4 a is fastened and fixedto the lower portions of front side frames 4 b and the lower portion ofa dash panel 4 c at the rear ends thereof.

The power transmission mechanism 14 is configured to transmit thedriving force generated by the engine 12 to the rear wheels 2 a, whichare the main drive wheels. As illustrated in FIG. 1 to FIG. 3 , thepower transmission mechanism 14 includes a propeller shaft 14 aconnected to the engine 12, a clutch 14 b, and a transmission 14 c,which is a stepped transmission. The propeller shaft 14 a extends fromthe engine 12 disposed in the front portion of the vehicle 1 toward therear of the vehicle 1 in a propeller shaft tunnel 4 d (FIG. 2 ). Therear end of the propeller shaft 14 a is connected to the transmission 14c via the clinch 14 b, The output shaft of the transmission 14 c isconnected to the axle shaft (not illustrated) of the rear wheels 2 a anddrives the rear wheels 2 a.

In the embodiment, the transmission 14 c is provided in so-calledtransaxle arrangement. As a result, since the main body of thetransmission with a large outer diameter is not present immediatelybehind the engine 12, the width of the floor tunnel (propeller shafttunnel 4 d) can be reduced, the foot space in the middle of the occupantcan be obtained, and the lower body of the occupant can take asymmetrical posture that faces directly the front. Furthermore, theouter diameter and the length of the main drive motor 16 can easily havesufficient sizes according to the output power thereof while keepingthis posture of the occupant.

The main drive motor is an electric motor for generating a driving forcefor the main drive wheels, provided on the body of the vehicle 1,disposed behind the engine 12 adjacently to the engine 12, and functionsas a body side motor. In addition, an inverter (INV) 16 a is disposedadjacently to the main drive motor 16 and the inverter 16 a converts thecurrent from the battery 18 into alternating current and supplies thealternating current to the main drive motor 16. Furthermore, asillustrated in FIG. 2 and FIG. 3 , the main drive motor 16 is connectedin series to the engine 12 and the driving force generated by the maindrive motor 16 is also transmitted to the rear wheels 2 a via the powertransmission mechanism 14. Alternatively, the present invention may beconfigured so that the driving three is transmitted to the rear wheels 2a via a part of the power transmission mechanism 14 by connecting themain drive motor 16 to an intermediate point of the power transmissionmechanism 14. In addition, the embodiment adopts, as the main drivemotor 16, a 25 kW permanent magnet motor (permanent magnet synchronousmotor) driven by 48 V.

The battery 18 is an electric storage unit that stores electric powerfor mainly operating the main drive motor 16. In addition, asillustrated in FIG. 2 , the battery 18 is disposed inside the propellershaft tunnel 4 d so as to surround the torque tube 14 d that covers thepropeller shaft 14 a below the vehicle interior of the vehicle 1 in theembodiment. Furthermore, in the embodiment, a 48 V 3.5 kWh lithium ionbattery (LIB) is used as the battery 18.

Since the transaxle arrangement is adopted in the embodiment asdescribed above, the volume for accommodating the battery 18 can beexpanded toward the space in front of the floor tunnel (propeller shafttunnel 4 d) created by this arrangement. This can obtain and expand thecapacity of the battery 18 without reducing the space in the middle ofthe occupant by increasing the width of the floor tunnel. Alternatively,the battery 18 may be disposed in the rear portion of the vehicle 1 in amodification.

As illustrated in FIG. 4 , the auxiliary drive motors 20, which arefront wheel motors, are provided in the front wheels 2 b under thesprings of the vehicle 1 so as to generate driving forces for the leftand right front wheels 2 b, which are the auxiliary drive wheels. In theembodiment, the front wheel 2 b is supported by a double wishbone typesuspension and is suspended by an upper arm 8 a, a lower arm 8 b, aspring 8 c, and a shock absorber 8 d. The auxiliary drive motors 20 arein-wheel motors and are housed in the wheels of the front wheels 2 b.Accordingly the auxiliary drive motors 20 are provided in the so-called“under-spring portions” of the vehicle 1 so as to drive the front wheels2 b. In addition, as illustrated in FIG. 1 , the current from thecapacitor (CAP) 22 is converted into alternating current by inverters 20a and supplied to the auxiliary drive motors 20. Furthermore, in theembodiment, the auxiliary drive motors 20 are not provided withdeceleration machines that are deceleration mechanisms, the drivingforces of auxiliary drive motors 20 are directly transmitted to thefront wheels 2 b, and the wheels are directly driven. In addition, inthe embodiment, 17 kW induction motors are adopted as the auxiliarydrive motors 20.

The capacitor (CAP) 42 is provided so as to store the electric powerregenerated by the auxiliary drive motors 20. As illustrated in FIG. 2and FIG. 3 , the capacitor 22 is disposed between the left and rightfront wheels 2 b immediately its front of (ahead of) the engine 12 andsupplies electric power to the auxiliary drive motors 20 provided in thefront wheels 2 b of the vehicle 1. That is, the capacitor 22 is disposedat a position at which the capacitor 22 overlaps with the front wheels 2b when viewed from the side of the vehicle 1 as illustrated in FIG. 3and at least a part of the capacitor 22 overlaps with the engine 12 whenviewed from the front of the vehicle 1 as illustrated in FIG. 2 . Asillustrated in FIG. 4 , in the capacitor 22, brackets 22 a projectingfrom both side surfaces thereof are supported by the from side frames 4b via a capacitor mount 6 b. In addition, a harness 22 b extending fromthe auxiliary drive motor 20 to the capacitor 22 passes through theupper end of the side wall of the wheel house and is led to the engineroom. In addition, the capacitor 22 is configured to store electriccharge at a voltage higher than in the battery 18 and is disposed in aregion between the left and right front wheels 2 b, which are theauxiliary drive wheels. The auxiliary drive motors 20, which are drivenmainly by the electric power stored in the capacitor 22, are driven by avoltage higher than in the main drive motor 16.

The control device 24 controls the engine 12, the main drive motor 16,and the auxiliary drive motors 20 to execute a motor travel mode and aninternal combustion engine travel mode. Specifically, the control device24 can include a microprocessor, a memory, an interface circuit, aprogram for operating these components (these components are notillustrated), and the like. Details on control by the control device 24will be described later.

In addition, as illustrated in FIG. 1 , a high voltage DC/DC converter26 a and a low voltage DC/DC converter 26 b, which are voltageconverting units, are disposed near the capacitor 22. The high voltageDC/DC converter 26 a, the low voltage DC/DC converter 26 b, thecapacitor 22, and the two inverters 20 a are unitized to form anintegrated unit.

Next, the overall structure, the power supply structure, and the drivingof the vehicle 1 by the individual motors in the hybrid drive device 10according to the first embodiment of the present invention will bedescribed with reference to FIG. 5 to FIG. 8 .

FIG. 5 is a block diagram illustrating the inputs and outputs of varioussignals in the hybrid drive device 10 according to the first embodimentof the present invention. FIG. 6 is a block diagram illustrating thepower supply structure of the hybrid drive device 10 according to thefirst embodiment of the present invention. FIG. 7 is a diagramschematically illustrating one example of changes in voltages whenelectric power is regenerated into the capacitor 22 in the hybrid drivedevice 10 according to the embodiment. FIG. 8 is a diagram illustratingthe relationship between the output power of the motors used in thehybrid drive device 10 according to the embodiment and the vehiclespeed.

First, the inputs and outputs of various signals in the hybrid drivedevice 10 according to the first embodiment of the present inventionwill be described. As illustrated in FIG. 5 , the control device 24receives the detection signals detected by a mode selection switch 40, avehicle speed sensor 42, an accelerator position sensor 44, a brakesensor 46, an engine RPM sensor 48, an automatic transmission (AT) inputrotation sensor 50, an automatic transmission (AT) output rotationsensor 52, a voltage sensor 54, and a current sensor 56. In addition,the control device 24 controls the inverter 16 a for the main drivemotor, the inverters 20 a for the auxiliary drive motors 20, the highvoltage DC/DC converter 26 a, the low voltage DC/DC converter 26 b, afuel injection valve 58, a spark plug 60, and a hydraulic solenoid valve62 of the transmission 14 c by control signals to these components.

Next, the power supply structure of the hybrid drive device 10 accordingto the first embodiment of the present invention will be described. Asillustrated in FIG. 6 , the battery 18 and capacitor 22 included in ehybrid drive device 10 are connected in series to each other. The maindrive motor 16 is driven by approximately 48 V, which is the referenceoutput voltage of the battery 18, and the auxiliary drive motors 20 aredriven by a maximum voltage of 120 V, which is higher than the sum ofthe output voltage (inter-terminal voltage) of the battery 18 and theinter-terminal voltage of the capacitor 22. That is, in the embodiment,the maximum inter-terminal voltage of the capacitor 22 is 72 V, which ishigher than the inter-terminal voltage of the battery 18. Therefore, theauxiliary drive motors 20 are always driven by the electric powersupplied via the capacitor 22.

In addition, the inverter 16 a is mounted to the main drive motor 16 andconverts the output of the battery 18 into alternating current throughwhich the main drive motor 16, which is a permanent magnet motor, isdriven. Similarly, the inverters 20 a are mounted to the auxiliary drivemotors 20 and convert the outputs of the battery 18 and the capacitor 22into alternating current through which the auxiliary drive motors 20,which are induction motors, are driven. Since the auxiliary drive motors20 are driven by a voltage higher than in the main drive motor 16, theharness (electric wires) 22 b that supply electric power to theauxiliary drive motors 20 need to have high insulation. However, sincethe capacitor 22 is disposed close to the auxiliary drive motors 20, anincrease in the weight due to high insulation of the harnesses 22 b canbe minimized.

Furthermore, when, for example, the vehicle 1 decelerates, the maindrive motor 16 and the auxiliary drive motors 20 function as generatorsand generate electric power by regenerating the kinetic energy of thevehicle 1. The electric power regenerated by the main drive motor 16 isstored in the battery 18 and the electric power regenerated by theauxiliary drive motors 20 is stored mainly in the capacitor 22.

In addition, the high voltage DC IDC converter 26 a, which is a firstvoltage converting unit, is connected between the battery 18 and thecapacitor 22 and this high voltage DC/DC converter 26 a charges thecapacitor 22 by raising the voltage of the battery 18 when the electriccharge stored in the capacitor 22 is insufficient (when theinter-terminal voltage of the capacitor 22 drops), In contrast, when theinter-terminal voltage of the capacitor 22 rises to a predeterminedvoltage or higher due to regeneration of energy by the auxiliary drivemotors 20, the battery 18 is charged by reducing the electric chargestored m the capacitor 22 and applying the electric charge to thebattery 18. That is, the electric power regenerated by the auxiliarydrive motors 20 is stored in the capacitor 22, and then the battery 18is charged with a part of the stored electric charge via the highvoltage DC/DC convener 26 a.

Furthermore, the low voltage DC/DC converter 26 b, which is a secondvoltage converting unit, is connected between the battery 18 and 12Velectric components 25 of the vehicle 1. Since the control device 24 ofthe hybrid drive device 10 and many of the electric components 25 of thevehicle 1 operate at a voltage of 12 V, the electrical charge stored inthe battery 18 is lowered to 12 V by the low voltage DC/DC converter 26b and supplied to these devices.

Next, charging and discharging of the capacitor 22 will be describedwith reference to FIG. 7 .

As illustrated in FIG. 7 , the voltage of the capacitor 22 is the sum ofthe base voltage of the battery 18 and the inter-terminal voltage of thecapacitor 22 itself. When, for example, the vehicle 1 decelerates, theauxiliary drive motors 20 regenerate electric power and the capacitor 22is charged with the regenerated electric power. When the capacitor 22 ischarged, the inter-terminal voltage rises relatively rapidly. When theinter-terminal voltage of the capacitor 22 rises to a predeterminedvoltage or more due to the charging, the voltage of the capacitor 22 isreduced by the high voltage DC/DC converter 26 a and the battery 18 ischarged. As illustrated in FIG. 7 , the charging to the battery 18 fromthe capacitor 22 is performed relatively slowly than the charging to thecapacitor 22 and the voltage of the capacitor 22 drops to a propervoltage relatively slowly.

That is, the electric power regenerated by the auxiliary drive motors 20is temporarily stored in the capacitor 22 and then the battery 18 isslowly charged with the regenerated electric power. Depending on thetime when the regeneration is performed, the regeneration of electricpower by the auxiliary drive motors 20 may overlap with the chargingfrom the capacitor 22 to the battery 18.

In contrast, the battery 18 is directly charged with the electric powerregenerated by the main drive motor 16.

Next, the relationship between the vehicle speed and the output power ofthe motors in the hybrid drive device 10 according to the firstembodiment of the present invention will be described with reference toFIG. 8 . FIG. 8 is a graph illustrating the relationship between thespeed of the vehicle 1 and the output power of the motors in the hybriddrive device 10 according to the embodiment. In FIG. 8 , the outputpower of the main drive motor 16 is represented by a dotted line, theoutput power of one of the auxiliary drive motors 20 is represented by adot-dash line, the sum of the output power of the two auxiliary drivemotors 20 is represented by a dot-dot-dash line, and the sum of theoutput power of all motors is represented by a solid line. Although FIG.8 illustrates the speed of the vehicle 1 on the horizontal axis and theoutput power of the motors on the vertical axis, since there is acertain relationship between the speed of the vehicle 1 and the numberof revolutions of each of the motors, the output power of the motorsdraws curves similar to those in FIG. 8 even when the number ofrevolutions of each of the motors is represented on the horizontal axis.

Since a permanent magnet motor is adopted as the main drive motor 16 inthe embodiment, as represented by the dotted line in FIG. 8 , the outputpower of the main drive motor 16 is large in a low vehicle speed rangein which the number of revolutions of the motor is low and the motoroutput power that can be output reduces as the vehicle speed increases.That is, in the embodiment, the main drive motor 16 is driven byapproximately 48 V, outputs a torque (maximum torque) of approximately200 Nm up to approximately 1000 rpm, and the torque reduces with theincrease in the number of revolutions at approximately 1000 rpm or more.In addition, in the embodiment, the main drive motor 16 is configured toobtain a continuous output power of approximately 20 kW and a maximumoutput power of approximately 25 kW in the lowest low speed range.

In contrast, since induction motors are used as the auxiliary drivemotors 20, the output power of the auxiliary drive motors 20 is verysmall in the low vehicle speed range, the output power increases as thespeed becomes higher, the maximum output power is obtained at a vehiclespeed close to 130 km/h or so, and then the motor output power reduces,as represented by the dot-dash line and the dot-dot-dash line in FIG. 8. In the embodiment, the auxiliary drive motors 20 are driven byapproximately 120 V, and each of them obtains an output power ofapproximately 17 kW and the two motors obtain a total output power ofapproximately 34 kW at a vehicle speed close to 130 km/h or so. That is,in the embodiment, each of the auxiliary drive motors 20 has a peak ofthe torque curve and obtains a maximum torque of approximately 200 Nm atapproximately 600 to 800 rpm.

The solid line in FIG. 8 represents the sum of the output power of themain drive motor 16 and the two auxiliary drive motors 20. As is clearfrom this graph, in the embodiment, a maximum output power ofapproximately 53 kW is obtained at a vehicle speed close to 130 km/h orso and the travel condition requested in the WLTP test at this vehiclespeed is satisfied at this maximum output power. In addition, althoughthe output power values of the two auxiliary drive motors 20 are summedup even in the low vehicle speed range as represented by the solid linein FIG. 8 , the auxiliary drive motors 20 are actually not driven in thelow vehicle speed range as described later. That is, the vehicle isdriven only by the main drive motor 16 at startup and in a low vehiclespeed range and the two auxiliary drive motors 20 generate output poweronly when large output power is required in the high vehicle speed range(for example, when the vehicle 1 is accelerated in the high vehiclespeed range). By using the induction motors (auxiliary drive motors 20)capable of generating large output power in the high revolutions rangeonly in the high speed range as described above, sufficient output powercan be obtained when necessary (for example, when acceleration at apredetermined speed or more is performed) while an increase in vehicleweight is kept low.

Next, the structure of the auxiliary drive motors 20 adopted in thehybrid drive device 10 according to the first embodiment of the presentinvention will be described with reference to FIG. 9 . FIG. 9 is asectional view schematically illustrating the structure of the auxiliarydrive motor 20.

As illustrated in FIG. 9 , the auxiliary drive motor 20 is an outerrotor type induction motor including a stator 28 and a rotor 30 thatrotates around this stator.

The stator 28 includes a substantially discoid, stator base 28 a, astator shaft 28 b extending from the center of the stator base 28 a, anda stator coil 28 c attached around the stator shaft 28 b. In addition,stator coil 28 c is housed in an electrical insulating liquid chamber32, immersed in electrical insulating liquid 32 a that fills theelectrical insulating liquid chamber, and subject to boiling cooling viathe liquid.

The rotor 30 is formed in a substantially cylindrical shape so as tosurround the periphery of the stator 28 and has a substantiallycylindrical rotor body 30 a with one end closed and a rotor coil 30 bdisposed on the inner peripheral wall surface of the rotor body 30 a.The rotor coil 30 b is disposed facing the stator coil 28 c so as togenerate induction current by the rotational magnetic field generated bythe stator coil 28 c. In addition, the rotor 30 is supported by abearing 34 attached to the end of the stator shaft 28 b so as to rotatesmoothly around the stator 28.

The stator base 28 a is supported by an upper arm 8 a and a lower arm 8b (FIG. 4 ) that suspend the front wheels of the vehicle 1. In contrast,the rotor body 30 a is directly fixed to the wheels of the front wheels2 b (not illustrated). Alternating current converted by the inverters 20a flows through the stator coil 28 c and generates a rotational magneticfield. This rotational magnetic field causes an induced current to flowthrough the rotor coil 30 b and generates a driving force that rotatesthe rotor body 30 a. As described above, the driving forces generated bthe auxiliary drive motors 20 rotationally drive the wheels of the frontwheels 2 b (not illustrated) directly.

Next, the operation of the motor travel mode and the operation of theinternal combustion engine travel mode performed by the control device24 will be described with reference to FIG. 10 and FIG. 11 . FIG. 10 isa flowchart illustrating control by the control device 24 and FIG. 11 isa graph illustrating examples of the operations of these modes. Theflowchart illustrated in FIG. 10 is repeatedly executed at predeterminedtime intervals while the vehicle 1 operates.

The graph illustrated in FIG. 11 represents, in order from the top, thespeed of the vehicle 1, the torque generated by the engine 12, thetorque generated by the main drive motor 16, the torque generated by theauxiliary drive motors 20, the voltage of the capacitor 22, the currentof the capacitor 22, and the current of the battery 18. In the graphrepresenting the torque of the main drive motor 16 and the torques ofthe auxiliary drive motors 20, positive values mean the state in whichmotors generate torques and negative values mean the state in whichmotors regenerate the kinetic energy of the vehicle 1. In addition, inthe graph representing the current of the capacitor 22 and the currentof the battery 18, negative values mean the state in which electricpower is supplied (discharged) to motors and positive values mean thestate of charging with the electric power regenerated by motors.

First, in step S1 in FIG. 10 , it is determined whether the vehicle 1has been set to the internal combustion engine travel mode (ENG mode).That is, the vehicle 1 has the mode selection switch 40 (FIG. 5 ) thatselects either the internal combustion engine travel mode or the motortravel mode (EV mode) and it is determined in step S1 which mode hasbeen set. Since the motor travel mode is set at time t₁ in FIG. 11 , theprocessing of the flowchart in FIG. 10 proceeds to step S2.

Next, in step S2, it is determined whether the speed of the vehicle 1 isequal to or more than a predetermined vehicle speed the processingproceeds to step S6 when the speed is equal to or more than thepredetermined vehicle speed or the processing proceeds to step S3 whenthe speed is less than the predetermined vehicle speed. Since the driverhas started the vehicle 1 and the vehicle speed is low at time t₁ inFIG. 11 , the processing of the flowchart proceeds to step S3.

Furthermore, in step S3, it is determined whether the vehicle 1 isdecelerating (whether the brake pedal (not illustrated) of the vehicle 1is being operated). The processing proceeds to step S5 when the vehicle1 is decelerating or the processing proceeds to step S4 when the vehicle1 is accelerating or traveling at a constant speed (when the brakesensor 46 (FIG. 5 ) does not detect the operation of the brake pedal).Since they driver has started the vehicle 1 and is accelerating thevehicle 1 (accelerator position sensor 44 (FIG. 5 ) has detected thatthe accelerator pedal of the vehicle 1 has been operated by apredetermined amount or more) at time t₁ in FIG. 11 , the processing ofthe flowchart proceeds to step S4 and the processing of the flowchart inFIG. 10 is completed once. In step S4, the main drive motor 16 generatesa torque and the vehicle speed increases (from time t₁ to time t₂ inFIG. 11 ). At this time, since discharge current flows from the battery18 that supplies electric power to the main drive motor 16 and dischargecurrent from the capacitor 22 remains zero because the auxiliary drivemotors 20 do not generate torques, the voltage of the capacitor 22 doesnot change. The current and voltage are detected by the voltage sensor54 and the current sensor 56 (FIG. 5 ) and input to the control device24. In addition, from time t₁ to time t₂ in FIG. 11 , the engine 12 isnot driven because the motor travel mode is set. That is, since thecontrol device 24 stops fuel injection via the fuel injection valve 58of the engine 12 and does not perform ignition via the ignition plug 60,the engine 12 does not generate a torque.

In the example illustrated in FIG. 11 , the vehicle 1 accelerates fromtime t₁ to time t₂ and then travels at a constant speed until time t₃.In this period, the processing of steps S1, S2, S3, and S4 in theflowchart in FIG. 10 is repeatedly executed. During this low speedtravel, the torque generated by the main drive motor 16 becomes smallerthan the torque during the acceleration, the current discharged from thebattery 18 also becomes smaller.

Next, when the driver operates the brake pedal (not illustrated) of thevehicle 1 at time t₃ in FIG. 11 , the processing of the flowchart inFIG. 10 proceeds to step S5 from step S3. In step S5, the driving by themain drive motor 16 is stopped (no torque is generated) and the kineticenergy of the vehicle 1 is regenerated as electric power by theauxiliary drive motors 20. The vehicle 1 is decelerated by theregeneration of the kinetic energy, the discharge current from battery18 becomes zero, the charge current flows through the capacitor 22because the electric power is regenerated by the auxiliary drive motors20, and the voltage of the capacitor 22 rises.

When the vehicle 1 stops at time t₄ in FIG. 11 , the charge current tothe capacitor 22 becomes zero and the voltage of the capacitor 22 alsobecomes constant. Next, the vehicle 1 is started again at time t₅ andreaches a constant speed travel (time t₆), and the processing of stepsS1, S2, S3, and S4 in the flowchart in FIG. 10 is repeatedly executeduntil the deceleration of the vehicle 1 is started (time t₇). When thedeceleration of the vehicle is started at time the processing of stepsS1, S2, S3, and S5 in the flowchart in FIG. 10 is repeatedly executedand the auxiliary drive motors 20 regenerate electric power. Asdescribed above, the motor travel mode is set while the vehicle startsand stops repeatedly at a relatively low speed in urban areas or thelike, the vehicle 1 functions purely as an electric vehicle (EV) and theengine 12 does not generate a torque.

Furthermore, when the vehicle 1 is started at time t₈ in FIG. 11 , theprocessing of steps S1, S2, S3, and S4 in the flowchart in FIG. 10 isrepeatedly executed and the vehicle 1 is accelerated. Next, when thespeed of the vehicle 1 detected by the vehicle speed sensor 42 (FIG. 5 )exceeds a predetermined first vehicle speed at time t₉, the processingof the flowchart proceeds to step S6 from step S2. In step S6, it isdetermined whether the vehicle 1 is decelerating (the brake pedal isbeing operated). Since the vehicle 1 is not decelerating at time t₉, theprocessing of the flowchart proceeds to step S7. In step S7, it isdetermined whether the vehicle 1 is accelerating by a predeterminedvalue or more (whether the accelerator pedal of the vehicle 1 has beenoperated by a predetermined amount or more). In the embodiment, thepredetermined first vehicle speed is set to approximately 100 km/h,which is more than a travel speed of 0 km/h.

Since the vehicle 1 is accelerating by a predetermined value or more attime t₉ in the example illustrated in FIG. 11 , the processing proceedsto step S8, in which the main drive motor 16 is driven and the auxiliarydrive motors 20 are also driven. When the vehicle 1 is accelerated by apredetermined value or more at the predetermined first vehicle speed ormore in the motor travel mode as described above, electric power issupplied to the main drive motor 16 and the auxiliary drive motors 20 toobtain the required power, and this drives the vehicle 1. In otherwords, the control device 24 starts the vehicle 1 (time t₈) by causingthe main drive motor 16 to generate a driving force and then causes theauxiliary drive motors 20 to generate driving forces when the travelspeed of the vehicle 1 detected by the vehicle speed sensor 42 reachesthe first vehicle speed (time t₉). At this time, the battery 18 supplieselectric power to the main drive motor 16 and the capacitor 22 supplieselectric power to the auxiliary drive motors 20. Since the capacitor 22supplies electric power as described above, the voltage of the capacitor22 drops. While the vehicle 1 is driven by the main drive motor 16 andthe auxiliary drive motors 20 (from time t₉ to time t₁₀), the processingof steps S1, S2, S6, S7, and S8 in the flowchart is repeatedly executed.

As described above, the auxiliary drive motors 20 generate drivingforces when the travel speed of the vehicle 1 is equal to or more thanthe predetermined first vehicle speed and are prohibited from generatingdriving forces when the travel speed is less than the first vehiclespeed. Although the first vehicle speed is set to approximately 100 km/hin the embodiment, the first vehicle speed may be set to any vehiclespeed that is equal to or more than approximately 50 km/h according tothe output characteristics of the adopted auxiliary drive motors 20. Incontrast, the main drive motor 16 generates a driving force when thetravel speed of the vehicle 1 is less than a predetermined secondvehicle speed including zero or when the travel speed is equal to ormore than the second vehicle speed. The predetermined second vehiclespeed may be set to a vehicle speed identical to or different from thefirst vehicle speed. In addition, in the embodiment, the main drivemotor 16 always generates a driving force when the driving force isrequested in the motor travel mode.

Next, when the vehicle 1 shifts to a constant speed travel (when theaccelerator pedal is operated by less than, a predetermined amount) attime t₁₀, in FIG. 11 , the processing of steps S1, S2, S6, S7, and S9 inthe flowchart is repeatedly executed. In step S9, driving by theauxiliary drive motors 20 is stopped (no torque is generated) and thevehicle 1 is driven only by the main drive motor 16. Even when thevehicle 1 travels at the predetermined vehicle speed or more, thevehicle 1 is driven only by the main drive motor 16 if the accelerationis less than the predetermined amount.

In addition, since the voltage of the capacitor 22 drops to thepredetermined value or less because the capacitor 22 has driven theauxiliary drive motors 20 from time t₉ to time t₁₀, the control device24 sends a signal to the high voltage DC/DC converter 26 a at time t₁₀to charge the capacitor 22. That is, the high voltage DC/DC converter 26a raises the voltage of the electric charge stored in the battery 18 andcharges the capacitor 22. This causes the current for driving the maindrive motor 16 and the current for charging the capacitor 22 to bedischarged from the battery 18 from time t₁₀ to time t₁₁ in FIG. 11 . Iflarge electric power is regenerated by the auxiliary drive motors 20 andthe voltage of the capacitor 22 rises to a predetermined value or more,the control device 24 sends a signal to the high voltage DC/DC converter26 a to reduce the voltage of the capacitor 22 and charges the battery18. As described above, the electric power regenerated by the auxiliarydrive motors 20 is consumed by the auxiliary drive motors 20, or storedin the capacitor 22 and then used to charge the battery 18 via the highvoltage DC/DC converter 26 a.

When the vehicle 1 decelerates (the brake pedal is operated) at time t₁₁in FIG. 11 , the processing of steps S1, S2, S6, and S10 in theflowchart will be repeatedly executed. In step S10, the kinetic energyof the vehicle 1 is regenerated as electric power by both the main drivemotor 16 and the auxiliary drive motors 20. The electric powerregenerated by the main drive motor 16 is stored in the battery 18 andthe electric power regenerated by the auxiliary drive motors 20 isstored in the capacitor 22. As described above, when the brake pedal isoperated at the specified vehicle speed or more, electric power isregenerated by both the main drive motor 16 and the auxiliary drivemotors 20 and electric charge is stored in the capacitor 22 and thebattery 18.

Next, at time t₁₂ in FIG. 11 , the driver switches the mode of thevehicle 1 from the motor travel mode to the internal combustion enginetravel mode by operating the mode selection switch 40 (FIG. 5 ) anddepresses the accelerator pedal (not illustrated). When the mode of thevehicle 1 is switched to the internal combustion engine travel mode theprocessing of the flowchart in FIG. 10 by the control device 24 proceedsto step S11 from step S1, and the processing of step S11 and subsequentsteps is executed.

First, in step S11, it is determined whether the vehicle 1 stops. Whenthe vehicle 1 does not stop (the vehicle 1 is traveling), it isdetermined in step S12 whether the vehicle 1 is decelerating (whetherthe brake pedal (not illustrated) is being operated). Since the vehicle1 is traveling and the driver is operating the accelerator pedal at timet₁₂ in FIG. 11 , the processing of the flowchart in FIG. 10 proceeds tostep S13.

In step S13, the supply of fuel to the engine 12 starts and the engine12 generates a torque. That is, since the output shaft (not illustrated)of the engine 12 is directly connected to the output shaft (notillustrated) of the main drive motor 16 in the embodiment, the outputshaft of the engine 12 always rotates together with driving by the maindrive motor 16. However, the engine 12 does not generate a torque in themotor travel mode because fuel supply to the engine 12 is performed,but, in the internal combustion engine travel mode, the engine 12generates a torque because fuel supply (fuel injection by the fuelinjection valve 58 and ignition by the ignition plug 60) starts.

In addition, immediately after switching from the motor travel mode tothe internal combustion engine travel mode, the control device 24 causesthe main drive motor 16 to generate a torque for starting the engine(from time t₁₂ to time t₁₃ in FIG. 11). This torque for starting theengine is generated to cause the vehicle 1 to travel until the engine 12actually generates a torque after fuel supply to the engine 12 isstarted and suppress torque fluctuations before and after the engine 12generates a torque. In addition, in the embodiment, when the number ofrevolutions of the engine 12 at the time of switching to the internalcombustion engine travel mode is less than a predetermined number ofrevolutions, fuel supply to the engine 12 is not started and the fuelsupply is started when the number of revolutions of the engine 12 isequal to or more than the predetermined number of revolutions due to thetorque for starting the engine. In the embodiment, when the number ofrevolutions of the engine 12 detected by the engine RPM sensor 48 risesto 2000 rpm or more, fuel supply is started.

While the vehicle 1 accelerates or travels at a constant speed after theengine 12 is started, the processing of steps S1, S11, S12, and S13 inthe flowchart in FIG. 10 is repeatedly executed (from time t₁₃ to timet₁₄ in FIG. 11 ). As described above, in the internal combustion enginetravel mode, the engine 12 exclusively outputs the power for driving thevehicle 1 and the main drive motor 16 and the auxiliary drive motors 20do not output the power for driving the vehicle 1. Accordingly, thedriver can enjoy the driving feeling of the vehicle 1 driven by theinternal combustion engine.

Next, when the driver operates the brake pedal (not illustrated) at timet₁₄ in FIG. 11 , the processing of the flowchart in FIG. 10 proceeds tostep S14 from step S12. In step S14, fuel supply to the engine 12 isstopped and fuel consumption is suppressed. Furthermore, in step S15,the main drive motor 16 and the auxiliary drive motors 20 regenerate thekinetic energy of the vehicle 1 as electric energy and charge currentflows through the battery 18 and the capacitor 22. As described above,during deceleration of the vehicle 1, the processing of steps S1, S11,S12, S14, and S15 is repeatedly executed (from time t₁₄ to time t₁₅ inFIG. 11 ).

During deceleration of the vehicle 1 in the internal combustion enginetravel mode, the control device 24 performs downshift torque adjustmentby driving the auxiliary drive motors 20 in switching (shifting) of thetransmission 14 c, which is a stepped transmission. The torque generatedby this torque adjustment complements an instantaneous torque drop orthe like and is not equivalent to the torque that drives the vehicle 1.Details on torque adjustment will be described later.

On the other hand, when the vehicle 1 stops at time t₁₅ in FIG. 11 , theprocessing of the flowchart FIG. 10 proceeds to step S16 from step S11.In step S16, the control device 24 supplies the minimum fuel required tomaintain the idling of the engine 12. In addition, the control device 24generates an assist torque via the main drive motor 16 so that theengine 12 can maintain idling at a low number of revolutions. Asdescribed above, while the vehicle 1 stops, the processing of steps S1,S11, and S16 is repeatedly executed (from time t₁₅ to time t₁₆ in FIG.11 ).

Although the engine 12 is a flywheel-less engine in the embodiment,since the assist torque generated by the main drive motor 16 acts as apseudo flywheel, the engine 12 can maintain smooth idling at a lownumber of revolutions. In addition, adoption of a flywheel-less enginemakes the response of the engine 12 high during a travel in the internalcombustion engine travel mode, thereby enabling driving with a goodfeeling.

In addition, when the vehicle 1 starts from a stop state in the internalcombustion engine travel mode, the control device 24 increases thenumber of revolutions the main drive motor 16 (the number of revolutionsof the engine 12) to a predetermined number of revolutions by sending asignal to the main drive motor 16. After the number of revolutions ofthe engine is increased to the predetermined number of revolutions, thecontrol device 24 supplies the engine 12 with fuel for driving theengine, causes the engine 12 to perform driving, and performs a travelin the internal combustion engine travel mode.

Next, torque adjustment during switching (shifting) of the transmission14 c will be described with reference to FIG. 12 .

FIG. 12 is a diagram that schematically illustrates changes in theacceleration that acts on the vehicle when transmission 14 c downshiftsor upshifts, and represents, in order from the top, examples ofdownshift torque down, downshift torque assistance, and upshift torqueassistance.

In the internal combustion engine travel mode, the hybrid drive device10 according to the first embodiment of the present invention causes thecontrol device 24 to automatically switch the clutch 14 b and thetransmission 14 c, which is an automatic transmission, according to thevehicle speed and the number of revolutions of the engine when theautomatic shift mode is set. As illustrated in the upper part of FIG. 12, when the transmission 14 c downshifts (shifts to a low speed) withnegative acceleration acting on the vehicle 1 during deceleration (timet₁₀₁ in FIG. 12 ), the control device 24 disconnects the clutch 14 b todisconnect the output shaft of the engine 12 from the main drive wheels(rear wheels 2 a). When the engine 12 is disconnected from the maindrive wheels in this way, since the rotation resistance of the engine 12no longer acts on the main drive wheels, the acceleration acting on thevehicle 1 instantaneously changes to a positive side, as indicated bythe dotted line in the upper part of FIG. 12 . Next, the control device24 sends a control signal to the transmission 14 c and switches thebuilt-in hydraulic solenoid valve 62 (FIG. 5 ) to increase the reductionratio of the transmission 14 c. Furthermore, when the control device 24connects the clutch 14 b at time t₁₀₂ at which the downshift iscompleted, the acceleration changes to a negative side again. Althoughthe period from the start to the completion of a downshift (from timet₁₀₁ to time t₁₀₂) is generally 300 to 1000 msec, the occupant is givenan idle running feeling and may have a discomfort feeling due to aso-called torque shock in which the torque acting on the vehicleinstantaneously changes.

In the hybrid drive device 10 according to the embodiment, the controldevice 24 makes torque adjustment by sending a control signal to theauxiliary drive motors 20 at the time of a downshift to suppress theidle running feeling of the vehicle 1. Specifically, when the controldevice 24 performs a downshift by sending a signal to the clutch 14 band the transmission 14 c, the control device 24 reads the number ofrevolutions of the input shaft and the number of revolutions of theoutput shaft of the transmission 14 c detected by the automatictransmission input rotation sensor 50 and the automatic transmissionoutput rotation sensor 52 (FIG. 5 ), respectively. Furthermore, thecontrol device 24 predicts changes in the acceleration generated in thevehicle 1 based on the number of revolutions of the input shaft and thenumber of revolutions of the output shaft that have been read and causesthe auxiliary drive motors 20 to regenerate energy. This suppresses aninstantaneous rise in the acceleration (change to the positive side) ofthe vehicle 1 due to a torque shock as indicated by the solid line inthe upper part of FIG. 12 , thereby suppressing an idling runningfeeling. Furthermore, in the embodiment, the torque shock in the maindrive wheels (rear wheels 2 a) caused by a downshift is complemented bythe auxiliary drive wheels (front wheels 2 b) via the auxiliary drivemotors 20. Accordingly, torque adjustment can be made without beingaffected by the dynamic characteristics of the power transmissionmechanism 14 that transmits power from the engine 12 to the main drivewheels.

In addition, as indicated by the dotted line in the middle part of FIG.12 , when downshift is started at time t₁₀₃ with positive accelerationacting on the vehicle 1 during acceleration, the output shaft of theengine 12 is disconnected from the main drive wheels (rear wheels 2 a).Accordingly, since the drive torque by the engine 12 does not act on therear wheels 2 a and a torque shock occurs, the occupant may be given astall feeling by the time the downshift is completed at time t₁₀₄. Thatis, the acceleration of the vehicle 1 instantaneously changes to thenegative side at time t₁₀₃ at which a downshift is started and theacceleration changes to the positive side at time t₁₀₄ at which thedownshift is completed.

In the hybrid drive device 10 according to the embodiment, whenperforming a downshift, the control device 24 predicts changes in theacceleration caused in the vehicle 1 based on detection signals from theautomatic transmission input rotation sensor 50 and the automatictransmission output rotation sensor 52 and causes the auxiliary drivemotors 20 to generate driving forces. As indicated by the solid line inthe middle part of FIG. 12 , this suppresses an instantaneous drop(change to the negative side) of the acceleration of the vehicle 1 by atorque shock and suppresses a stall feeling.

Furthermore, as indicated by the dotted line in the lower part of FIG.12 , when an upshift is started at time t₁₀₅ with positive accelerationacting on the vehicle 1 (positive acceleration reduces with time) duringacceleration, the output shaft of the engine 12 is disconnected from themain drive wheels (rear wheels 2 a). Accordingly, since the drive torqueby the engine 12 does not act on the rear wheels 2 a and a torque shockoccurs, the occupant may be given a stall feeling by the time theupshift is completed at time t₁₀₆. That is, the acceleration of thevehicle 1 instantaneously changes to the negative side at time t₁₀₅ atwhich the upshift is started and the acceleration chances to thepositive side at time t₁₀₆ at which the upshift is completed.

In the embodiment, when performing a upshift, the control device 24predicts changes in the acceleration caused in the vehicle 1 based ondetection signals from the automatic transmission input rotation sensor50 and the automatic transmission output rotation sensor 52 and causesthe auxiliary drive motors 20 to generate driving forces. As indicatedby the solid line in the lower part of FIG. 12 , this suppresses aninstantaneous drop (change to the negative side) of the acceleration ofthe vehicle 1 due to a torque shock and suppresses a stall feeling.

As described above, the adjustment of the drive torque by the auxiliarydrive motors 20 during a downshift or an upshift of the transmission 14c is performed in a very short time and does not substantially drive thevehicle 1. Therefore, the power generated by the auxiliary drive motors20 can be generated by the electric charge regenerated by the auxiliarydrive motors 20 and stored in the capacitor 21. In addition, theadjustment of the drive torque by the auxiliary drive motors 20 can beapplied to an automatic transmission with a torque converter, anautomatic transmission without a torque converter, an automated manualtransmission, and the like.

In the hybrid drive device 10 according to the first embodiment of thepresent invention, since the voltage of the battery and the capacitorconnected in series is applied to the auxiliary drive motors 20, whichare the front wheel motors (FIG. 6 ), the auxiliary drive motors 20 canbe driven by a higher voltage even when the battery 18 of a low voltageis used. This can keep the current for driving the auxiliary drivemotors 20 low and prevent the conductor for supplying electric powerfrom becoming excessive. On the other hand, since a high voltage isapplied to the auxiliary drive motors 20 from the battery 18 andcapacitor 22 connected in series, the dielectric withstand voltage of ahigh voltage portion needs to be high. However since the auxiliary drivemotors 20 are close to the capacitor 22 disposed between the left andright wheels 2 b of the vehicle (FIG. 1 ), the route requested for ahigh dielectric withstand voltage becomes short and an increase inweight and cost can be minimized.

In addition, in the hybrid drive device 10 according to the embodiment,since the capacitor 22 is disposed at a position at which at least apart of the capacitor 22 overlaps with the from wheels 2 b when viewedfrom the side of the vehicle 1 (FIG. 3 ), the electric power supply pathfrom the capacitor 22 to the auxiliary drive motors 20 can be furthershortened, thereby further suppressing an increase in weight and costcaused by the insulating member.

Furthermore, in the hybrid drive device 10 according to the embodiment,since the capacitor 22 is disposed in front of the engine 12 (FIG. 2 ),if the vehicle 1 collides from the front, the capacitor 22 is damagedfirst. The capacitor is generally made of a material that does not burneasily. Accordingly, even if the vehicle 1 collides, since theflame-retardant capacitor 22 suppresses damage to the engine 12, thesafety of the vehicle 1 can be further enhanced.

In addition, in the hybrid drive device 10 according to the embodiment,since the auxiliary drive motors 20, which are the front wheel motors,are in-wheel motors, the drive shafts that connect the auxiliary drivemotors 20 and the wheels can be eliminated or shortened, thereby makingthe vehicle 1 more lightweight.

Furthermore, in the hybrid drive device 10 according to the embodiment,since the battery 18 is disposed below the vehicle interior of thevehicle 1, even if the vehicle 1 collides from the front, the impact ofthe collision does not easily affect the battery 18 and damage to thebattery 18 can be suppressed.

In addition, in the hybrid drive device 10 according to the embodiment,since the maximum inter-terminal voltage of the capacitor 22 is higherthan the inter-terminal voltage of the battery 18 (FIG. 7 ), the voltageapplied to the auxiliary drive motors 20 can be sufficiently high andsufficient output power can be obtained while the current flowing to theauxiliary drive motors 20 is suppressed.

Furthermore, since the hybrid drive device 10 according to theembodiment includes the high voltage DC/DC converter 26 a, which is thefirst voltage converting unit that charges the capacitor 22 with theelectric power stored in the battery 18 and charges the battery 18 withthe electric power stored in the capacitor 22, the amounts of electricpower stored in the battery 18 and the capacitor 22 can be adjusted andthe electric power stored in the battery 18 and the capacitor 22 can beused effectively.

In addition, in the hybrid drive device 10 according to the embodiment,since the low voltage DC/DC converter 26 b, which is the second voltageconverting unit, reduces the voltage of the battery 18 and supplieselectric power to the electric components 25, the battery 18 used todrive the main drive motor 16 and the auxiliary drive motors 20 can beshared with the electric components 25 provided in the vehicle 1 and thevehicle 1 can be made lightweight.

The vehicle drive device according to the first embodiment of thepresent invention has been described above. Although the vehicle drivedevice according to the present invention is applied to an FR vehicle inthe first embodiment described above, the present invention isapplicable to various types of vehicles such as a so-called FF vehiclein which an engine and/or a main drive motor are disposed in the frontportion of the vehicle and the front wheels are the main drive wheels ora so-called RR vehicle in which an engine and/or a main drive motor aredisposed in the rear portion of the vehicle and the rear wheels are themain drive wheels.

Although preferred embodiments of the present invention have beendescribed above, various modifications can be made to the embodimentsdescribed above. In particular, the present invention is applied to ahybrid drive device including an engine and a motor in the embodimentsdescribed above, but the present invention is applicable to a vehicledrive device that drives a vehicle only by a motor without having anengine.

REFERENCE SIGNS LIST

-   -   1: vehicle    -   2 a: rear wheel (main drive wheel)    -   2 b: front wheel (auxiliary drive wheel)    -   4 a: subframe    -   4 b: front side frame    -   4 c: dash panel    -   4 d: propeller shaft tunnel    -   6 a: engine mount    -   6 b: capacitor mount    -   8 a: upper arm    -   8 b: lower arm    -   8 c: spring    -   8 d: shock absorber    -   10: hybrid drive device (vehicle drive device)    -   12: engine (internal combustion engine)    -   14: power transmission mechanism    -   14 a: propeller shaft    -   14 b: clutch    -   14 c: transmission (stepped transmission, automatic        transmission)    -   14 d: torque tube    -   16: main drive motor (main drive electric motor, body side        motor)    -   16 a: inverter    -   18: battery (electric storage unit)    -   20: auxiliary drive motor (front wheel motor, in-wheel motor)    -   20 a inverter    -   22: capacitor    -   22 a: bracket    -   22 b: harness    -   74: control device (controller)    -   75: electric component    -   26 a: high voltage DC/DC converter (first voltage converting        unit)    -   26 b: low voltage DC/DC converter (second voltage converting        unit)    -   28: stator    -   28 a: stator base    -   28 b: stator shaft    -   28 c: stator coil    -   30: rotor    -   30 a: rotor body    -   30 b: rotor coil    -   32: electrical insulating liquid chamber    -   32 a: electrical insulating liquid    -   34: bearing    -   40: mode selection switch    -   42: vehicle speed sensor    -   44: accelerator position sensor    -   46: brake sensor    -   48: engine RPM sensor    -   50; automatic transmission input rotation sensor    -   52: automatic transmission output rotation sensor    -   54: voltage sensor    -   56: current sensor    -   58: fuel injection valve    -   60: spark plug    -   62: hydraulic solenoid valve    -   101: vehicle    -   102 a: front wheel (main drive wheel)    -   102 b rear wheel (auxiliary drive wheel)    -   202 a: front wheel (main drive wheel)    -   301: vehicle    -   302 b: rear wheel (main drive wheel)

The invention claimed is:
 1. A vehicle drive device for a vehicle, thevehicle drive device comprising: a front wheel motor for driving frontwheels of the vehicle; a battery and a capacitor that supply electricpower for driving the front wheel motor; and an internal combustionengine that drives the vehicle, wherein a voltage of the battery and thecapacitor connected in series is applied to the front wheel motor, thecapacitor is disposed between the left and right front wheels of thevehicle, the capacitor is disposed in front of the internal combustionengine so that at least a part of the capacitor overlaps with theinternal combustion engine when viewed from a front of the vehicle, thecapacitor further comprises brackets, each of the brackets protrudingfrom each side of the capacitor in the vehicle width direction, and thecapacitor is supported by a front side frame via a capacitor mount. 2.The vehicle drive device according to claim 1, wherein the capacitor isdisposed at a position at which at least a part of the capacitoroverlaps with the front wheels when viewed from a side of the vehicle.3. The vehicle drive device according to claim 1, wherein the frontwheel motor includes in-wheel motors provided in the left and rightfront wheels of the vehicle, respectively.
 4. The vehicle drive deviceaccording to claim 1, wherein a maximum inter-terminal voltage of thecapacitor is adjusted to a voltage higher than an inter-terminal voltageof the battery.
 5. The vehicle drive device according to claim 1,further comprising: a first voltage converting unit connected betweenthe capacitor and the battery, wherein the first voltage converting unitperforms at least one of an operation that raises the voltage of thebattery and charges the capacitor with electric power stored in thebattery and an operation that lowers the voltage of the capacitor andcharges the battery with electric power stored in the capacitor.
 6. Thevehicle drive device according to claim 1, further comprising: a secondvoltage converting unit connected between the battery and an electriccomponent provided in the vehicle, wherein the second voltage convertingunit lowers the voltage of the battery and supplies electric power tothe electric component.
 7. The vehicle drive device according to claim1, wherein the width of the capacitor is longer than the width of theinternal combustion engine in the vehicle width direction, when viewedfrom a front of the vehicle.
 8. The vehicle drive device according toclaim 1, wherein the internal combustion engine is installed on asubframe of the vehicle via engine mounts, the subframe being fastenedto the front side frame.
 9. The vehicle drive device according to claim1, wherein the capacitor is made of a flame-retardant material.
 10. Ahybrid driving apparatus configured to drive a vehicle, the hybriddriving apparatus comprising: a front wheel motor for driving frontwheels of the vehicle; a battery that supply electric power for drivingthe front wheel motor; a capacitor that supply electric power fordriving the front wheel motor, the capacitor being disposed between theleft and right front wheels of the vehicle in the vehicle widthdirection and disposed in front of the internal combustion engine sothat at least a part of the capacitor overlaps with the internalcombustion engine when viewed from a front of the vehicle, the capacitorcomprising brackets, each of the brackets protruding from each side ofthe capacitor in the vehicle width direction, and being supported by afront side frame via a capacitor mount; an internal combustion enginethat drives the vehicle; and circuitry configured to control a voltageof the battery and the capacitor connected in series to be applied tothe front wheel motor.
 11. The hybrid driving apparatus according toclaim 10, wherein the capacitor is disposed at a position at which atleast a part of the capacitor overlaps with the front wheels when viewedfrom a side of the vehicle.
 12. The hybrid driving apparatus accordingto claim 10, wherein the front wheel motor includes in-wheel motorsprovided in the left and right front wheels of the vehicle,respectively.
 13. The hybrid driving apparatus according to claim 10,wherein the circuitry is configured to set a maximum inter-terminalvoltage of the capacitor which is higher than an inter-terminal voltageof the battery.
 14. The hybrid driving apparatus according to claim 10,further comprising: a first voltage converter connected between thecapacitor and the battery, wherein the circuitry is configured tocontrol the first voltage converter to perform at least one of anoperation that raises the voltage of the battery and charges thecapacitor with electric power stored in the battery, and an operationthat lowers the voltage of the capacitor and charges the battery withelectric power stored in the capacitor.
 15. The hybrid driving apparatusaccording to claim 10, further comprising: a second voltage converterconnected between the battery and an electric component provided in thevehicle, wherein the circuitry is configured to control the secondvoltage converter to lower the voltage of the battery and supplieselectric power to the electric component.
 16. The hybrid drivingapparatus according to claim 10, wherein the width of the capacitor islonger than the width of the internal combustion engine in the vehiclewidth direction, when viewed from a front of the vehicle.
 17. Hybriddriving apparatus according to claim 10, wherein the internal combustionengine is installed on a subframe of the vehicle via engine mounts, thesubframe being fastened to the front side frame.
 18. Hybrid drivingapparatus according to claim 10, wherein the capacitor is made of aflame-retardant material.